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Arjun's PM copy-Microbiology and Infection > MI: GI infections > Flashcards

MI: GI infections Flashcards

1
Q

List some reportable GI infections

A
  • Camplybacter
  • Salmonella
  • Shigella
  • Escherichia coli O157
  • Listeria
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2
Q

What are the main characteristics of secretory diarrhoea? What are some causes?

A
  • No fever/low grade fever
  • No inflammatory cells in stool
  • Causes: Vibrio Cholera, ETEC
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3
Q

What are the main characteristics of inflammatory diarrhoea? What are some causes?

A
  • Fever
  • Inflammatory cells present in stool (neutrophils)
  • Causes: Campylobacter jejuni, Shigella, non-typhiodal Salmonella, EIEC

Also known as exudative diarrhoea

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4
Q

List some examples of severe GI infections that produce a fever with little stool changes.

A

Also known as enteric fever

  • Salmonella typhi
  • Enteropathogenic Yersinia
  • Brucella

White blood cells are present in stool (mononuclear cells)

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5
Q

Describe the mechanism by which Vibrio cholerae causes secretory diarrhoea.

A
  • The cholera toxin has subunits A and B which stimulate adenylate cyclase.
  • This leads to the production of cAMP which opens chloride channels on the membranes of enterocytes.
  • Chloride efflux into the lumen is accompanied by water and electrolyte loss.
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6
Q

What are superantigens?

A
  • Toxins that bind to TCR and MHC outside the peptide binding region
  • This leads to non-specific activation and large-scale polyclonal expansion of T cells with massive cytokine production
  • Results in systemic toxicity and suppression of adaptive immune response
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7
Q

How does the host immune response determine in inflammatory respone to enteropathic bacteria?

A
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8
Q

What type of organism is Staphylococcus aureus?

A
  • Gram-positive coccus
  • Catalase and coagulase positive
  • Appears in clusters
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9
Q

What type of toxin is produced by Staphylococcus aureus?

A

Enterotoxin - this is an exotoxin that can act as a superantigen in the GI tract triggering the release of IL1 and IL2

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10
Q

How is Staphylococcus aureus spread and what kind of GI symptoms can it cause?

A
  • Spread by skin lesions on food handlers
  • Causes prominent nausea and vomiting (occasionally watery diarrhoea)
  • Self-limiting (resolution within 24 hours) so does not require treatment
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11
Q

What type of organisms is Bacillus cereus?
Associated food?

A

Gram-positive rods that are spore-forming

Spores germinate in reheated rice

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12
Q

What type of toxins does B. cereus produce?

A
  • Heat-stable emetic toxin
  • Heat-labile diarrhoeal toxin
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13
Q

What type of GI symptoms does B. cereus cause?

A

Diarrhoeal type - watery, non-bloody diarrhoea; abdominal cramping

Emetic type - nausea and vomiting (sometime diarrhoea as well)

NOTE: it can cause bacteraemia and cerebral abscesses in vulnerable populations

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14
Q

Name three types of Clostridium infection

A
  • Clostridium botulinum
  • Clostridium perfringens
  • Clostridium difficile
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15
Q

What kind of infection does Clostridium botulinum cause?

Associated foods?

Treatment?

A

Causes botulism - ptosis, double vision, dysphagia, progessive muscle weakness and paralysis

  • From canned food
  • Causes disease due to preformed toxin which blocks acetylcholine release at peripheral nerve synapses resulting in paralysis
  • Treated with antitoxin
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16
Q

What kind of infection does Clostridium perfringens cause?

A

Causes food poisoning - watery diarrhoea, cramps, but NO vomiting that lasts 24 hours

  • From undercooking and poor storage of meat
  • Part of normal colonic flora, but NOT small bowel
  • Creates enterotoxic superantigen affects small bowel
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17
Q

What kind of infection does C. difficile cause?

A

Pseudomembranous colitis

  • Hospital-acquired infection related to antibiotic use
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18
Q

Which antibiotics are most commonly implicated in C. difficile colitis?

A
  • Cephalosporins
  • Clindamycin
  • Ciprofloxacin
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19
Q

How is C. difficile colitis treated?

A
  • Metronidazole, vancomycin
  • Stop the offending antibiotic
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20
Q

What type of organism is Listeria monocytogenes?

A
  • Gram positive, rod-shaped, facultative anaerobe
  • Beta-haemolytic, aesculin-positive with tumbling motility
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21
Q

What is the source of Listeria?

A

Grows are 4 degrees so refrigerated foods (cold enhancement)

  • Unpasteurised dairy
  • Vegetables
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22
Q

What GI symptoms does Listeria tend to cause? Which patients groups are particularly susceptible?

A
  • Fever, watery diarrhoea, cramps, headache and NO vomiting
  • Neonates, immunocompromised
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23
Q

How is Listeria infection treated?

A

Ampicillin

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24
Q

What type of organisms are Enterobacteriaceae and name some examples?

A
  • Facultative anaerobes
  • Lactose fermenters
  • Oxidase-negative
  • Escherichia coli, Salmonella, Shigella, Klebsiella
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25
Q

Name and describe the different types of E. coli infection.

A
  • ETEC - toxigenic, main cause of travellers’ diarrhoea
  • EPEC - pathogenic, infantile diarrhoea
  • EIEC - invasive, dysentry
  • EHEC - haemorrhagic, caused by E. coli 0157:H7

Avoid antibiotic treatment

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26
Q

Where does E. coli act?

A

Jejunum, ileum but NOT colon

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27
Q

Which toxin causes haemolytic uraemic syndrome?

A

EHEC shiga-like verocytotoxin

28
Q

What type of bacteria are Salmonellae?

A
  • Gram-negatives, Non-lactose fermenting,
  • Produce hydrogen suphide (form black colonies)
  • Grows on TSI agar, XLD agar and selenite F broth
29
Q

Which antigens are found on Salmonellae?

A
  • LPS O antigen (groups A-I)
  • Flagellar H antigen
  • Capular Vi antigen (virulence, antiphagocytic)

NOTE: differences in these antigens help identify the serotypes of Salmonellae

30
Q

List 2 main species of Salmonella.

A
  • Salmonella typhi
  • Salmonella enterica
31
Q

What are 2 important serotypes of S. enterica?

A
  • Salmonella enterica serotype Enteritidis
  • Salmonella enterica serotype Typhimurium
32
Q

How is Salmonella Enteritidis transmitted?

A

Via infected poultry, eggs, meat

33
Q

Describe the presentation of Salmonella Enteritidis.

A

Causes enterocolitis - self-limiting diarrhoea that is non-bloody

  • Bacteraemia is rare
  • Usually no treatment required
34
Q

How is Salmonella typhi transmitted?

A
  • Transmitted only by humans (faeco-oral)
  • Multiplies in Peyer’s patches and spreads via the endoreticular system
35
Q

Describe the presentation of Salmonella typhi.

A

Causes typhoid fever with constipation
(rose coloured spots)

36
Q

Which subset of patients are at increased risk of Salmonella bacteraemia?

A

Sickle cell patients

37
Q

How is Salmonella typhi treated?

A

Ceftriaxone

38
Q

What are some key microbiological features of Shigella?
(stains etc)

A
  • Gram negative
  • Non-lactose fermenter
  • Does NOT produce hydrogen suphide
  • Non-motile
39
Q

Which antigens are seen on Shigella?

A

LPS O antigens

Polysaccharide (groups A-D) used to identify species

40
Q

List some types of Shigella.

A
  • Shigella sonnei
  • Shigella dysenteriae
  • Shigella flexneri (MSM)
41
Q

What is the most effective bacterial enteric pathogen and why?

A

Shigella - it has the lowest infective dose (50)

NOTE: Shigella has no animal reservoir and no carriers state

42
Q

How does Shigella infection manifest? How do you treat it?

A

Dysentry

  • Severe diarrhoea with blood and mucus in the faeces
  • Invades the cells of the distal ileum and colon
  • Produces shiga toxin

Avoid antibiotics when treating, however use ciprofloxacin if required

43
Q

What are the microbiological features of Vibrio Cholerae?

A
  • Gram-negative
  • Comma-shaped
  • Late lactose-fermenters
  • Oxidase-positive
44
Q

What are the different groups of Vibrio cholerae?

A
  • O1 - causes epidemics
  • Non-O1 - sporadic, non-pathogens
45
Q

How is Vibrio cholerae transmitted?

A

Contamination of water and food from human faeces

46
Q

What type of GI disturbance does Vibrio cholerae cause and how do you treat it?

A
  • Produces massive watery (secretory) diarrhoea without inflammatory cells
  • Treat by replacing the water and electrolytes lost
47
Q

Name and describe the key features of other types of Vibrio.
How is it treated?

A

Vibrio parahaemolyticus:

  • Caused by ingestion of raw/undercooked seafood
  • Causes self-limiting diarrhoea (3 days)
  • Grows on salty agar

Vibrio vulnificus:

  • Causes cellulitis in shellfish handlers
  • Can cause fatal septicaemia with diarrhoea and vomiting in HIV patients

Treat both with doxycycline

48
Q

What are the main microbiological features of Campylobacter?

A
  • Gram negative
  • Comma-shaped
  • Microaerobphilic
  • Oxidase-positive
  • Motile
49
Q

How is Campylobacter transmitted?

A

Transmitted via ingestion of food and water contaminated with animal faeces

50
Q

Describe the presentation of Campylobacter jejuni infection.

A
  • Watery, foul-smelling diarrhoea, bloody stools, fever and severe abdominal pain
51
Q

How is Campylobacter infection treated?

A

Only treated if immunocompromised

  • Erythromycin or ciprofloxacin if presenting within first 4-5 days
52
Q

What are some complications of Campylobacter infection?

A

Guillian-Barre syndrome

Reactive arthritis

53
Q

Which other bacterial organisms can cause GI disease?

A

Yersinia enterocolitica

  • Non-lactose fermenting
  • Transmitted via food contaminated with faeces of domestic animals
  • Causes enterocolitis and mesenteric adenitis
  • Also associated with reactive arthritis

Mycobacteria (M. Tuberulosis, Avium, Intracellulare)

54
Q

What are the key characteristics of Entamoeba histolytica?

A
  • Motile trophozoite in diarrhoeal illness
  • Non-motile cyst in non-diarrhoeal illness
  • Killed by boiling, removed via water filters
  • Contains four nuclei
  • No animal reservoir
55
Q

Describe the pathophysiology of diarrhoeal illness caused by Entamoeba histolytica.

A

Ingestion of cysts → trophozoites move into the ileum → colonise the colon → causes flask-shaped ulcers

56
Q

Describe the presentation of GI infection by Entamoeba histolytica.

A
  • Dysentry
  • Flatulence
  • Tenesmus
  • Liver abscess

Chronic infection can cause weightloss +/- diarrhoea

57
Q

How is Entamoeba histolytica infection diagnosed and treated?

A
  • Diagnosis: stool microscopy (wet-mount, iodine and trichrome), serology of invasive disease
  • Treatment: metronidazole + paromomycin
58
Q

What are the key microbiological features of Giardia lamblia?

A
  • Pear-shaped trophozoites
  • Two nuclei
  • Four flagellae and a suction disc
59
Q

Outline the pathophysiology of GI disease caused by Giardia.

A
  • Transmitted by ingestion of cyst from faecally contaminated water
  • Excystation in the duodenum leads to trophozoite attachment
  • Results in malabsorption of protein and fat
60
Q

How does Giarda infection present?

A
  • Foul-smelling non-bloody diarrhoea,
  • Cramps, flatulence,
  • NO fever
61
Q

How is Giardia infection diagnosed and treated?

A
  • Stool microscopy
  • ELISA
  • String test
  • Treatment: metronidazole
62
Q

What are the main features of Cryptosporidium parvum?
What stain is used?

A
  • Protozoa that causes severe diarrhoea in the immunocompromised
  • Oocysts can be seen in the stool using modified Kinyoung acid fast stain
  • Treated by boosting the immune system
63
Q

What is the predominant strain of norovirus?

A

GII4

64
Q

What is rotavirus and what does it cause?

A
  • dsDNA virus
  • Replicates in the mucosa of the small intestine
  • Causes secretory diarrhoea with no inflammation

NOTE: exposure to natural infection twice will confer lifelong immunity

65
Q

List some other viruses that can cause diarrhoeal illnesses.

A
  • Adenovirus (types 40 and 41 can cause non-bloody diarrhoea in <2 year olds) - diagnosed via PCR or stool antigen detection
  • Poliovirus
  • Enterovirus (e.g. coxaskie, echovirus)
  • Hepatitis A

Transmitted via faeco-oral route

66
Q

Which causes of diarrhoeal illness have available vaccines?

A
  • Cholera (serogroup O1)
  • Campylobacter
  • ETEC
  • Salmonella typhi
  • Rotavirus - rotarix (live, monovalent), rotateq (pentavalent), rotashield (used if risk of intussusception)
67
Q

Who is responsible for collecting reports of diarrhoeal illness and identifying outbreaks?

A

Health Protection Unit (HPU)

Arjun's PM copy-Microbiology and Infection (26 decks)

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